Field of View (FOV)

For radiometric collectors, the range of angles over which they are sensitive to incoming light.  Usually expressed as the full-width half-maximum (FWHM), but sometimes as the half-angle.  For example, a receiver with a 10° FWHM FOV has 50% of its peak sensitivity at 5° from its central axis.  This could also be described as a 5° half-angle.